When to pitch additional Yeast???

[DrKennethNoisewater]

I keep reading that a lot of people seem to think one packet of a typical liquid yeast (in this case it's London YEast ESB 1968) is not enough to inoculate a 5-gallon batch. Dude at my home brew spot said that you can always pitch more yeast at any point of the fermentation process, but I wanted to see when the optimal time to do so would be.

I'm about 7 days into my primary, and was going to rack to a secondary on Monday (after 10 days). Would that be the best time to pitch some additional yeast, or should I just go ahead and do it now?

Initial gravity was a bit lower than it should have been.....

Also, does it need to be stirred or anything?

Thanks from a newbie....

 

[Denny]

Why are you going to pitch more yeast?

 

[kombat]

Underpitching stresses the yeast and causes it to produce off-flavours during the lag phase (the first couple of days) as it struggles to multiply to enough cells to ferment the batch. Pitching more yeast a week later is too late - those off flavours have already been created. You need to pitch enough yeast right from the get-go.

 

[kh54s10]

The ideal time to add more yeast is when you pitch the first time. After fermentation is at high krausen the yeast have already reproduced to the number required to ferment the beer. Adding any more will not do much. After fermentation has finished adding more will only add more yeast cells.

You would be wasting $$ and yeast if you added any at this point.

 

[Denny]

The ideal time to add more yeast is when you pitch the first time. After fermentation is at high krausen the yeast have already reproduced to the number required to ferment the beer. Adding any more will not do much. After fermentation has finished adding more will only add more yeast cells.

You would be wasting $$ and yeast if you added any at this point.

I agree with this, but why does the OP think he needs any more yeast? Hasn't the beer fermented out? He doesn't say.

 

[DrKennethNoisewater]

I wanted to pitch more yeast in an attempt to hopefully raise the gravity a little bit. I've often read (here) that one smack pack of liquid yeast is not enough to inoculate a five gallon batch.

My home brew guy here in town made it sound like there's no such thing as a bad time to pitch additional yeast, whether it's two days into fermentation or 10 days.

You guys disagree with that?

 

[DrKennethNoisewater]

I agree with this, but why does the OP think he needs any more yeast? Hasn't the beer fermented out? He doesn't say.

Like I mentioned, because I keep reading that one smack pack of liquid is not enough to properly inoculate a five gallon batch. I'm starting to believe it because my last two batches have turned out great flavor-wise, but the gravity has been lower in each case.

I suppose it could be something else I'm missing along the way, but not enough sugars seems like the culprit to me.

 

[BrewingGunner]

I wanted to pitch more yeast in an attempt to hopefully raise the gravity a little bit. I've often read (here) that one smack pack of liquid yeast is not enough to inoculate a five gallon batch.

My home brew guy here in town made it sound like there's no such thing as a bad time to pitch additional wyeast, whether it's two days into fermentation or 10 days.

You guys disagree with that?

Yeast has nothing to do with the gravity. Sugar is what adds to the gravity. Yeast eats the sugar and lowers the gravity.

 

[JonM]

Read up about making starters. I think that'll answer all your Qs.

 

[EarlyAmateurZymurgist]

Most amateur brewers fail to realize that yeast is the most important ingredient in brewing. Pitching a large healthy culture is necessary to prevent household bacteria from overwhelming one's pitching yeast during the growth phase. Brewers sanitize their equipment. Sanitizing is not the same thing as sterilizing. Santizing equipment merely reduces the amount of microflora present on one's fermenting gear down to level where one's pitching yeast has a chance of overwhelming it during the growth phase.

Ninety-nine percent of all beer infections are the result of poor yeast handling. Fermentation is little more than controlled spoilage. Bacteria cells divide every thirty minutes. Yeast cells divide every nineties minutes; therefore, one needs to pitch enough clean yeast to out compete any other microflora that may be introduced to one's wort. Cell division follows an exponential growth pattern; therefore, the increase in cell count for yeast can be calculated as:

initial_yeast_cell_count * 2^(elapsed_time_in_minutes_since_the_start_of_the_ growth_phase / 90), where the symbol ""^" denotes raised to the power of.

Examples

Yeast cell count after 90 minutes of growth

initial_yeast_cell_count * 2^(90 / 90) = 2 x initial_yeast_cell_count


Yeast cell count after 6 hours of growth

initial_yeast_cell_count * 2^(360 / 90) = 16 x initial_yeast_cell_count


There is a period between pitching and the growth phase (a.k.a. exponential or log phase) known as the lag phase. The lag phase is where the yeast cells that were pitched prepare themselves for growth.


With the above said, it is easy to now see why a Wyeast smack pack is far too little yeast to ensure a clean fermentation. Bacteria divide three times faster than yeast; therefore, a tiny amount bit of bacteria can completely overwhelm a yeast culture.

Examples

Yeast cell count after 6 hours of growth

initial_yeast_cell_count * 2^(360 / 90) = 16 x initial_yeast_cell_count


Bacteria cell count after 6 hours of growth

initial_bacteria_cell_count * 2^(360 / 30) = 4,096 x initial_bacteria_cell_count


Yeast cell count after 12 hours of growth

initial_yeast_cell_count * 2^(720 / 90) = 256 x initial_yeast_cell_count


Bacteria cell count after 12 hours of growth

initial_bacteria_cell_count * 2^(720 / 30) = 16,777,216 x initial_bacteria_cell_count


Yeast cell count after 24 hours of growth

initial_yeast_cell_count * 2^(1440 / 90) = 65,536 x initial_yeast_cell_count


Bacteria cell count after 24 hours of growth

initial_bacteria_cell_count * 2^(1440 / 30) = 281,474,976,710,656 x initial_bacteria_cell_count


In closing, the off flavors that result from underpitching have almost nothing to do with one's pitching yeast and everything to do with one's house microflora.

 

[BrewingGunner]

but not enough sugars seems like the culprit to me.

This is the gravity problem. Adding more yeast will NOT increase your gravity. In fact it will lower it as more yeast will eat more sugar.

 

[Denny]

Like I mentioned, because I keep reading that one smack pack of liquid is not enough to properly inoculate a five gallon batch. I'm starting to believe it because my last two batches have turned out great flavor-wise, but the gravity has been lower in each case.

I suppose it could be something else I'm missing along the way, but not enough sugars seems like the culprit to me.

But have you actually checked the gravity now that it's fermenting? You may not n1eed any more yeast at this point. I agree that with any beer over 1.040 a starter is a good thing and I always use one. But it's entirely possible that at this point you don't need any more yeast. Only a gravity check will tell you.